CN110831739B

CN110831739B - Extrusion head for extruding composite profiled elements and corresponding extrusion method

Info

Publication number: CN110831739B
Application number: CN201880043797.XA
Authority: CN
Inventors: M·鲁比; C·贝萨克
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2017-06-30
Filing date: 2018-06-28
Publication date: 2021-07-27
Anticipated expiration: 2038-06-28
Also published as: CN110831739A; EP3645236A1; US20200114565A1; US11440235B2; WO2019002782A1; EP3645236B1

Abstract

A method for co-extruding a composite Profile (PC) formed by assembling profiles (P1, P2) composed of different rubber mixtures (M1, M2), wherein the following steps are carried out by a co-extruder (1), said co-extruder (1) comprising an upstream extruder (30) and a downstream extruder (40) opening into an extrusion cavity formed by a space extending between a bottom wall (20) and a profile wall (11) of an extrusion head (2): -producing a first shaped part (P1) consisting of a first mixture (M1), said first shaped part (P1) comprising at least one shaped element intended to form a longitudinal insert (P10) and having a base (P13) which is integrally joined to the first shaped part (P1); -producing a composite shaped Part (PC) consisting of the first mixture and the second mixture; moving the insert between the walls (53, 54, 55) of the channel (5), said walls (53, 54, 55) extending in the longitudinal direction between the upstream forming plate (32) and the downstream forming plate (42) and forming a concave surface open towards the inside of the extrusion cavity, in such a way that the side walls (P11, P12) of the insert are joined to the second mixture only in the downstream gap.

Description

Extrusion head for extruding composite profiled elements and corresponding extrusion method

Technical Field

The present invention belongs to the field of extrusion of continuous shaped strips of rubber-based material, particularly intended for the manufacture of pneumatic tires.

More specifically, the invention relates to the extrusion of composite profiled elements consisting of an assembly having several profiled elements made of unvulcanized rubber compounds having different compositions. These composite profiled elements are produced in a known manner by using a coextrusion machine which employs several extruders which open into the production dome and comprise several forming gaps, which are arranged in such a way that the forming and final joining of the different profiled elements is performed by the same forming blade.

These composite profiled elements are particularly useful for producing tire treads.

Background

A cross-section of composite profiled element PC0 is shown in fig. 1. The radially inner first forming element P1 formed by compound M1 constitutes the bottom layer, and the second forming element P2 formed by compound M2 is the precursor portion of the tread intended to be in contact with the ground. The longitudinal grooves P20 are the precursor portions of the longitudinal grooves in the tire, disposed between the longitudinal ribs P21 in which blocks are molded that form the final tread pattern of the tire.

During the manufacture of the green tyre, the green tyre in endless form is covered with a length of strip taken from a continuous strip obtained using a coextrusion machine.

It is also known practice to use machines comprising co-extrusion heads to produce composite mouldings comprising a partial insert. These machines were developed to solve the problem of charge flow in vehicles after the emergence of silica-based compounds that do not function well as electrical conductors.

Document EP1448355 thus describes a co-extrusion machine comprising a roller and an extrusion head comprising at least two ducts for the flow of the underlayer rubber compound and the tread rubber compound, said ducts leading to extrusion holes through which the two (underlayer and tread) rubber compounds are discharged.

The extrusion head also comprises a micro-extruder of a third (conductive) rubber compound, equipped at its end with a nozzle passing through two flow conduits, so that the conductive third rubber compound is inserted into the base rubber compound and the tread rubber compound upstream of the extrusion orifice.

Publication EP 0925903 describes a so-called flat-head (roller-less) coextrusion machine comprising an extrusion head comprising a first channel for extruding the tread and a second channel for extruding a base layer considered to be electrically conductive. A third channel, arranged as a branch of the second channel, leads to a slotted opening arranged behind the extrusion orifice for forming a narrow conductive strip through the tread portion, which is a poor electrical conductor.

The invention also relates to the manufacture of a composite profiled element intended to form the tread of a tyre and comprising one or more inserts. These new treads, described for example in publication WO2016/202703, comprise anchoring elements intended to reinforce the tread blocks in the event of lateral loading of the tire.

The anchoring element may be formed from the same or a different compound from that from which the base layer is made.

The invention also relates to the manufacture of a composite profiled element intended to form the tread of a tyre, said profiled element being able to comprise structures of small thickness which form inserts or edge rubbers, the profile of which is disturbed without the presence of special implementation equipment.

Disclosure of Invention

For example, for protection and resistance reasons, it may prove advantageous to produce a tread in which the walls of the longitudinal grooves are covered with an edge rubber of small thickness, having a composition different from that of the compound forming the tread. In particular, this arrangement makes it possible to reduce the extension of the cuts associated with the attack or penetration of the gravel.

On the other hand, it may prove necessary to use an edge rubber of the type described above to protect the tread comprising the inserts provided near the edges of the groove.

According to the invention, a method is proposed for co-extruding a composite profiled element consisting of an assembly of profiled elements formed of different rubber compounds, wherein a co-extrusion machine is used comprising an upstream extruder and a downstream extruder conveying towards an extrusion chamber formed by a space between a lower wall of an extrusion head and a profiled wall arranged opposite to the lower wall.

The method implements the following steps, wherein:

conveying the first rubber compound coming out of the upstream extrusion conduit in the lower wall of the extrusion head upstream of a first forming blade, called "upstream forming blade", by using an upstream extruder,

-producing a first forming element formed of a first rubber compound in an upstream gap defined by an upstream forming blade and a forming wall, the first forming element comprising at least a first forming element portion intended to form a floor layer and at least a second forming element portion intended to form a longitudinal insert, the base of the longitudinal insert being in material continuity with the floor layer and the longitudinal insert forming a bulge on the floor layer, the side walls of the bulge extending outwardly with respect to the outer surface of the first forming element,

conveying the second rubber compound downstream of the upstream shaping blade via a downstream extrusion duct leading to the lower wall of the extrusion head, by using a downstream extruder, and combining the second rubber compound with the radially outer surface of the first shaping element at the region where the flow of the second rubber compound meets the flow of the first rubber compound,

-passing the first forming element and the second rubber compound through a downstream gap, provided downstream of the downstream extrusion duct and defined by a second forming blade and a forming wall, called "downstream forming blade", to produce a composite forming element formed by the first rubber compound and the second rubber compound.

The method is characterized in that the portion of the first rubber compound intended to form the insert circulates between the walls of the channel extending in the longitudinal direction between the upstream and downstream forming blades from the upstream end of the channel, which is located upstream of the converging flow of the first and second rubber compounds, up to the downstream end of the channel, which is located downstream of the converging flow and upstream of the downstream forming blade, the walls of the channels jointly forming a concave surface open towards the inside of the extrusion cavity and being arranged in such a way that the portion of the first rubber compound entering the channel and intended to form the insert, when proceeding longitudinally along the channel, remains in continuity in material with the underlayer and does not come into contact with the second compound, so that the bonding of the one or more side walls of the insert with the second rubber compound then takes place between the downstream space defined by the downstream forming blade and the forming wall In the gap.

Thus, the first compound coming from the upstream extruder enters the channel under pressure and maintains continuity on the material with the compound forming the bottom layer, since the concavity of the channel opens onto the side of said bottom layer disposed radially towards the inside with respect to the channel.

On leaving the second extrusion duct fed by the second extruder, the second compound is combined with the radially external surface of the first forming element in the longitudinal space located between the upstream forming blade and the downstream forming blade. Furthermore, the combination of these flows tends to produce a significant movement of material within the second compound in the radial or transverse direction, in particular when the first compound and the second compound have different rheological properties.

During the entire longitudinal progression along the passage between the outlet from the first forming blade and the inlet into the second forming blade, the portion of the first compound intended to form the insert is not in contact with the second compound, preventing the deformation of the profile of the insert caused by the second compound.

As a result, advantageously, the bonding of the side wall of the insert with the second compound then occurs only in the downstream interspace.

Thus, the method makes it possible to protect, in the dome portion formed by the lower wall and by the wall of the roll between the upstream and downstream gaps, the profile of the insert from the effects associated with the combination of the first forming element P1 and the second compound M2, which occurs in the zone located between the two gaps, creating turbulence associated with the pressure variations.

The method according to the invention may also comprise the following features, alone or in combination:

-a second compound is associated with each lateral wall of at least one insert.

-the second compound is associated with only one of the side walls of the at least one insert.

The cross section of the insert in a plane perpendicular to the longitudinal direction decreases between the outlet from the upstream gap and the inlet into the downstream gap, while proceeding along the channel.

At the entrance into the downstream gap, the insert has a triangular shape in cross-section in a plane perpendicular to the longitudinal direction.

Upon exiting the downstream gap, the outer apex of the insert is flush with the outer surface of the composite profiled element.

-extruding a first forming element without discontinuities in the transverse direction.

The total width of the first profiled element without discontinuities in the transverse direction amounts to more than half, more preferably at least 70% of the total width of the obtained composite profiled element PC.

The walls of the channel extend from the upstream gap to the downstream gap.

The profiled wall may be fixed, or

The lower wall of the extrusion head has a concave shape with a cylindrical profile extending with a given axis in the transverse direction, the circumferential direction of which coincides with the longitudinal direction defining the advancement direction of the profiled element through the machine, and the profiled wall is formed by a cylindrical roller which is rotatable about an axis coinciding with the axis of the lower wall and the radially outer wall of which forms said profiled wall,

the downstream profiled blade may comprise at least one protuberance to form a longitudinal groove in the composite profiled element, with an insert placed at the boundary of the side edges of the groove, such that the side walls of the insert form the edges of the groove, and a third rubber compound may be conveyed by using a secondary extruder via a secondary extrusion duct leading to the upstream portion of the protuberance, the secondary extrusion duct comprising a discharge opening provided at the edge of the protuberance, the discharge opening forming one or more side discharge openings, and a lower discharge opening, such that edge rubber can be applied in the groove of the composite profiled element, the edge rubber comprising a groove bottom edge rubber applied to the groove bottom by the lower discharge opening, and at least one side edge rubber applied to the insert side walls by the side discharge opening,

-forming the edge rubber using a third rubber compound having the same composition as the second rubber compound.

The method is also particularly suitable for manufacturing composite profiled elements for use as components in the production of tyres, in particular for use as treads for said tyres.

The method may be carried out by using a suitable extrusion head.

Such a head for extruding a composite profiled element constituted by an assembly of profiled elements formed of different rubber compounds is intended to be mounted on a co-extrusion machine by which the profiled element is advanced in an extrusion chamber along an extrusion direction extending from upstream to downstream and defining a longitudinal direction, said extrusion head comprising a lower wall partially delimiting said extrusion chamber and comprising, from upstream towards downstream of said lower wall in the longitudinal direction:

an upstream extrusion unit comprising an upstream extrusion duct placed at the outlet of the upstream extruder and opening into the lower wall,

-an upstream forming blade, arranged in a transverse direction downstream of the upstream extrusion duct, for determining a first transverse profile of the first forming element,

a downstream extrusion unit comprising, downstream of the upstream forming blade, a downstream extrusion duct placed at the outlet of the downstream extruder and opening into the lower wall,

-a downstream forming blade arranged in the transverse direction downstream of the downstream extrusion conduit for determining the transverse profile of the composite forming element.

The extrusion head is characterized in that it comprises at least one channel formed by walls extending in a longitudinal direction between an upstream forming blade and a downstream forming blade, said walls together forming a concave surface open towards the inside of the extrusion chamber and defining a duct open at its two longitudinal ends.

More specifically, the present invention relates to an extrusion head for extruding a composite profiled element consisting of an assembly of profiled elements formed with different rubber compounds, said extrusion head being intended to be mounted on a co-extrusion machine by which the profiled element is advanced in an extrusion chamber along an extrusion direction extending from upstream to downstream and defining a longitudinal direction, said extrusion head comprising a lower wall partially delimiting said extrusion chamber and comprising, from upstream towards downstream of said lower wall in the longitudinal direction:

an upstream extrusion unit comprising an upstream extrusion duct arranged at the outlet of the upstream extruder and opening into the lower wall, to enable the delivery of the first rubber compound stream,

-an upstream forming blade, arranged in a transverse direction downstream of the upstream extrusion duct, for determining a first transverse profile of a first forming element formed by said first flow of rubber compound,

a downstream extrusion unit comprising, downstream of the upstream forming blade, a downstream extrusion duct arranged at the outlet of the downstream extruder and opening into the lower wall, to enable the delivery and combination in a flow converging zone of a second stream of rubber compound with the first stream of rubber compound,

-a downstream forming blade, arranged in the transverse direction downstream of the downstream extrusion duct and the flow convergence zone, for determining the transverse profile of the composite forming element formed by the first rubber compound and the second rubber compound.

The extrusion head may be characterized in that it comprises at least one channel formed by a wall extending in a longitudinal direction between an upstream forming blade and a downstream forming blade from an upstream end of said channel upstream of the region where the flows of the first and second rubber compounds meet up to a downstream end of said channel downstream of said region where the flows meet and upstream of the downstream forming blade, said walls of the channels jointly forming a concave surface open towards the inside of the extrusion cavity and being arranged in such a way that, on the one hand, the part of the flow of the first rubber compound intended to form the insert in the composite forming element can enter and longitudinally advance in said channel and not come into contact with the second compound, but maintain continuity in material with the bottom layer of the first forming element made of the first rubber compound, the bottom layer will be formed in the upstream gap defined by the upstream forming blade, on the other hand, the bonding of the one or more side walls of the insert with the second rubber compound then takes place in the downstream gap defined by the downstream forming blade.

The extrusion head according to the invention may also comprise the following features, alone or in combination:

the upstream end of the channel is arranged in the continuation of the discharge opening formed in the upstream forming blade, while the downstream end of the channel emerges upstream of the downstream forming blade.

The concave duct of the channel is formed by the first and second side walls and the wall constituting the bottom of the channel.

The first and second side walls of the channel are supported by first and second side spacers, respectively, having a thickness of less than 2mm, preferably less than 1 mm.

At the downstream end of the channel, the wall forming the bottom of the channel is arranged at the same level as the wall of the downstream forming blade.

The cross section of the channel in a plane perpendicular to the longitudinal direction decreases continuously in a direction from the upstream end towards the downstream end of the channel, so that said cross section is smallest at the downstream end of the channel.

At the downstream end, the channel has a triangular shape in cross-section in a plane perpendicular to the longitudinal direction.

The downstream forming blade comprises at least one projection extending towards the inside of the extrusion cavity, said projection being intended to form a continuous longitudinal groove in the composite forming element.

At least one channel is present between two projections.

The downstream extruded duct comprises at least one dividing element extending longitudinally in longitudinal continuation of the projection between the upstream and downstream forming blades and dividing the downstream extruded duct into sub-ducts.

At least one channel comprises a side wall coinciding with a side wall of the separation element.

At the downstream forming blade, the inner wall of the dividing element is arranged at the same level as the inner wall of the projection in its continuation.

According to one preferred feature, which may constitute an entirely independent invention, alone or in combination with the above-mentioned features, the invention may relate to an extrusion head for extruding a composite profiled element constituted by an assembly of several profiled elements formed of different rubber compounds, said extrusion head being intended to be mounted on a co-extrusion machine by which the profiled elements are advanced in an extrusion chamber along an extrusion direction extending from upstream to downstream and defining a longitudinal direction, said head comprising a lower wall partially delimiting said extrusion chamber, and a downstream extrusion unit comprising a downstream profiling blade arranged in a transverse direction to determine the transverse profile of the composite profiled element formed by assembling the assembly with the profiled elements, said downstream profiling blade comprising at least one protuberance intended to form a groove in the composite profiled element, the extrusion head is characterized in that it comprises at least one auxiliary extrusion duct arranged at the outlet of the auxiliary extruder and opening into the upstream portion of the protuberance, the auxiliary extrusion duct comprising a lower discharge outlet and at least one side discharge outlet, which discharge outlets open respectively at the lower wall of the protuberance and at the edge of at least one side wall of the protuberance.

The side opening of the secondary extrusion conduit forms an opening through which compound from the secondary extruder is extruded to form an edge rubber on the bottom of the trough and at least one side wall of the trough. As can be seen subsequently, the thickness of such edge rubber can be adjusted by varying the position of the spacer (which supports the wall defining the auxiliary extrusion duct) and by varying the outlet cross-section of the side opening.

The particular layout of the auxiliary extrusion ducts provided in the downstream forming blade just upstream of the protuberances makes it possible to avoid the profile of the edge rubber of relatively small thickness being damaged during the coupling with the rubber or forming elements coming from the upstream part of the machine, which are intended to form the final composite forming element when assembled in the gap formed by the downstream forming blade.

-the auxiliary extrusion duct comprises at least one side wall laterally distanced from the side wall of the protuberancedSuch that the opening between the two walls defines a side vent.

The secondary extruded duct comprises an upstream wall substantially perpendicular to the longitudinal direction, wherein a plane passing through the lower edges of the upstream wall and the side walls in the secondary extruded duct is arranged at a position differing by a value from the position of the raised lower walleSuch that the opening between the plane and the lower wall of the projection defines a lower outlet row.

Advancing in a longitudinal direction from upstream towards downstream, the extrusion head further comprising,

an upstream extrusion unit comprising, upstream of the upstream forming blade, an upstream extrusion duct placed at the outlet of the upstream extruder and open to the lower wall,

a downstream extrusion unit comprising, downstream of the upstream forming blade and upstream of the downstream forming blade, a downstream extrusion duct placed at the outlet of the downstream extruder and open to said lower wall,

the downstream extruded duct comprises a dividing element extending longitudinally between the upstream forming blade and the downstream forming blade in a raised longitudinal continuation of the downstream forming blade and dividing the downstream extruded duct into sub-ducts.

Of course, it may be advantageous to combine, within the extrusion head, one or more of the above-described channels on the one hand, intended to shape one or more corresponding inserts made of the first compound and to prevent these inserts from being deformed by the second compound, with an opening on the other hand, which makes it possible to form an edge rubber, which in particular covers at least one of the side walls of the insert.

By this combination, it will be particularly advantageous that, on the one hand, it is possible to produce at least one insert arranged at the edge of the longitudinal groove of the composite profiled element to reinforce and stiffen the tread block of the tread as described above in the transverse direction, and on the other hand it is possible to cover the side walls of said insert adjacent to the longitudinal groove with a thin layer of edge rubber.

Preferably, the edge rubber covering the side walls of the insert adjacent to the grooves will have the same composition as the second compound constituting the tread blocks of the tread, which makes it possible to obtain a uniform composition of the tread, in particular for the walls delimiting said longitudinal grooves, and for the tread blocks of said tread, while maintaining the benefit of lateral fixing of the tread blocks provided by said insert.

This chemical homogeneity of the walls of the trench will make it possible in particular to easily introduce into said trench structure a flexible blade or baffle pattern intended to slow down the progression of the airborne noise associated with the ride along the trench, without thereby impeding the flow of water on wet roads; in particular, since the walls of the groove all have the same composition, it is advantageously possible to produce sets of flexible blades, each fixed to a different wall of the groove, without having to adjust the attachment method to match the composition of the wall concerned.

Indeed, the extrusion head according to the invention may exhibit the following characteristics, alone or in combination with each other or with one or the other of the preceding characteristics:

the extrusion head comprises one or more channels formed by lower walls

O a side wall of the chamber,

o a side wall disposed facing the previous side wall and formed by the side wall of the separation element, and

o a wall forming the bottom of the channel,

the walls extend in a longitudinal direction between the upstream and downstream forming blades, jointly forming a continuous concave surface opening radially towards the inside of the cavity and defining a duct which is open at its two longitudinal ends.

The downstream end of the channel opens into the inlet of the downstream forming blade, and the upstream end of the channel is arranged at the outlet of the upstream forming blade in continuation of the discharge opening formed in said upstream forming blade.

The side walls of the channels are supported by side spacers having a thickness of less than 2mm, preferably less than 1 mm.

At the downstream end, the wall forming the bottom of the channel is arranged at the same level as the wall of the downstream forming blade.

-the cross-section of the channel in a plane perpendicular to the longitudinal direction continuously decreases in a direction from the upstream end of the channel towards the downstream end of the channel, such that said cross-section of the channel is smallest at said downstream end.

At the downstream end, the channel is substantially triangular in cross-section in a plane perpendicular to the longitudinal direction.

More specifically, in addition to the above-described layout of the channel(s), the extrusion head may also comprise, alone or in combination with one or another of the features described above, a downstream forming blade comprising at least one protuberance to form a longitudinal groove in the composite forming element, and a channel arranged in such a way as to place an insert at the boundary of the side edges of the groove, so that the side walls of the insert form the walls of the groove, while the auxiliary extrusion duct comprises an outlet provided at the edge of the protuberance upstream of the protuberance, which outlet forms one or more side outlets, as well as a lower outlet, enabling the application of an edge rubber to the groove of the composite forming element, said edge rubber comprising a groove bottom edge rubber, applied on the bottom of the tread groove through the lower outlet, And at least one side edge rubber applied to the side wall of the insert through the side discharge opening.

The invention also relates to a machine for co-extruding profiled elements consisting of an assembly of profiled elements formed of different rubber compounds, comprising:

-an extrusion head according to any of the above-mentioned features,

a forming wall, arranged facing the lower wall of the extrusion head, forming a gap with the upstream forming blade and the downstream forming blade for extruding the forming element forming the composite forming element.

The forming wall may be fixed or, alternatively, the lower wall of the extrusion head has a concave shape with a cylindrical profile extending with a given axis in the transverse direction, the circumferential direction of said cylindrical profile coinciding with the longitudinal direction defining the advancement direction of the forming element in the extrusion chamber, and the forming wall is formed by the radially outer wall of a cylindrical roller rotatable about an axis coinciding with the axis of the lower wall.

Drawings

The invention will be better understood by studying the accompanying drawings, which are provided by way of example, and in no way limiting, and in which:

figure 1 shows the transverse profile of a composite profiled element according to the known prior art.

Figure 2 is a view in the transverse direction of an extrusion machine according to the invention.

Figure 3 is a cross-sectional view, in a plane perpendicular to the longitudinal direction, of a composite profiled element produced using an extrusion head according to a first embodiment of the present invention.

Figure 4 is a cross-sectional view, in a plane perpendicular to the longitudinal direction, of a composite profiled element produced using an extrusion head according to a second embodiment of the present invention.

Figure 5 is a schematic perspective view of an extrusion head according to a first embodiment of the invention.

FIG. 6 is a detail view of the circled extrusion head part of FIG. 5.

Figure 7 is a schematic perspective view of an extrusion head according to a second embodiment of the invention.

FIG. 8 is a detail of the circled extrusion head part of FIG. 7.

Figure 9 is a view in transverse direction of an alternative form of extrusion machine that can be used to implement the invention.

Fig. 10 is a cross-sectional view, on a plane perpendicular to the longitudinal direction, of a composite profiled element produced using an extrusion head according to a third embodiment in which openings are used for applying edge rubber to the walls of the tread groove.

Fig. 11 is a cross-sectional view, in a plane perpendicular to the longitudinal direction, of a composite profiled element produced using an extrusion head according to a fourth embodiment of the invention.

Figure 12 is a schematic perspective view of an extrusion head according to the third embodiment previously described.

FIG. 13 is a detail view of the circled extrusion head part of FIG. 12.

Figures 14 and 15 are detailed views of the encircled extrusion head of figure 13, showing the discharge opening of the auxiliary extrusion conduit.

Fig. 16 is a schematic perspective view of an extrusion head according to a fourth embodiment of the invention.

FIG. 17 is a detail view of the circled extrusion head part of FIG. 16.

Detailed Description

In a preferred embodiment of the invention, which serves as the basis of the present description, the coextrusion machine shown in fig. 2 comprises a cylindrical roller 10 which is rotated about an axis 12 by a drive assembly (not shown). The generatrix of the roll extends in the transverse direction DT and forms an extruded wall which is defined here by the radially outer wall 11 of the roll 10.

The extrusion head 2 includes: an upstream extrusion unit 3 and a downstream extrusion unit 4, said upstream extrusion unit 3 being associated with an extruder 30 supplying a first compound M1; the downstream extrusion unit 4 is associated with a downstream extruder 40 supplying a second compound M2.

Preferably, the invention applies to compounds M1, M2 that are based on rubber, in particular on rubber known as "raw" (i.e. unvulcanized rubber), which means that "rubber compounds" will preferably be mentioned in the following.

In this case, the invention can of course be applied to other types of first and second compounds M1, M2, in absolute terms, and in particular to any suitable polymer mixture, which can be different from the rubber-based compound.

Hereinafter, for the convenience of description, reference will be made without distinction to "compound" or "rubber compound".

The radially inner lower wall 20 of extrusion head 2 has an overall shape of a cylinder having an axis 12 and is arranged facing the radially outer wall 11 of roller 10. The space contained between the lower wall and the radially outer wall of the roll forms an extrusion cavity or dome in which the pressurized compound is shaped as it passes through a gap, in this case an upstream gap defined by the radially outer wall 11 of the roll 10 and the upstream forming blade 32, and a downstream gap defined by the radially outer wall 11 of the roll 10 and the downstream forming blade 42, respectively, the upstream forming blade 32 and the downstream forming blade 42 forming an integral part of the extrusion head.

At both lateral ends, the radial distance between the lower wall of the extrusion head 2 and the radially outer wall of the roller 10 is of the order of a few tenths of a millimeter, in order to limit the leakage of the rubber compound.

The roller 10 allows better driving of the composite profiled element in the extrusion process in the longitudinal direction DL and in particular may reduce edge effects at the base of the composite profiled element in contact with the radially outer wall 11 of the roller.

The composite profiled elements PC are oriented along the longitudinal direction DL on the conveyor belt 13 towards the downstream part of the extrusion machine.

Alternatively, the invention can be implemented entirely using a co-extrusion machine of the so-called flathead type, in which the extrusion wall is fixed, defining a gap with the upstream and downstream forming blades, and facing the lower wall of the extrusion head.

In order to make the following description clear, this alternative form of embodiment will be mentioned where necessary, taking into account the fact that: in most cases, any of the above with respect to the extrusion machine including the rollers, plus necessary modifications, are applicable to the flat head extruder.

Direction of rotation of the rollerRThe direction in which the profiled element advances in the extrusion chamber of the machine is determined, this direction being referred to as the longitudinal direction DL. Thus, the radial direction DR corresponds to a direction locally perpendicular to the transverse direction DT and the longitudinal direction DL, and the direction oriented radially towards the inside or the radially inner direction corresponds to a direction towards the inside of the extrusion cavity. Thus, when the first point is arranged in a radially lower position with respect to the second point, this means that the value of the distance between the first point and the second point, measured directionally in a direction from the center of the cavity towards the outside in a direction perpendicular to the longitudinal direction and the transverse direction, is a positive number. Likewise, using the same logic, the terms "lower" and "radially lower", the terms "higher" or "radially higher", the terms "outer" or "radially outer" or the terms "inner" or "radially inner" are considered equivalent.

Fig. 3 shows a first composite profiled element PC1 comprising a first profiled element P1 and a second profiled element P2; the first forming element P1 is made of a first compound M1 intended to form a radially inner first layer; the second forming element P2 is made of the second compound M2, intended to form a tread radially above the first layer formed by the first forming element P1.

The profile of the tread comprises longitudinal grooves P20, P20 being the precursor part of the tread grooves of the tire, P20 being interposed between longitudinal ribs P21 intended to form the tread blocks of the tread.

For convenience of description, the longitudinal groove P20 may be referred to as a longitudinal tread groove, the aforementioned groove being a precursor portion of the longitudinal tread groove.

The composite profiled element PC1 also comprises a longitudinal insert P10 made of the first compound M1, said longitudinal insert P10 here having a triangular overall shape and extending upwards in the radial direction DR from an imaginary base P13, said imaginary base P13 being located on the radially outer surface of the bottom layer P14 made of this same first compound M1. Here, the insert P10 extends up to the radially outer surface of the second forming element P2.

For simplicity and ease of description, a hypothetical distinction can be made by considering a first forming element P1, described below, said first forming element P1 comprising, on the one hand, a first forming element portion intended to form the bottom layer P14 and, on the other hand, a second forming element portion (or several second forming element portions) intended to form the insert P10 (or several inserts P10), even if these elements, the insert P10 and the bottom layer 14 are in fact preferably formed in a single piece with each other.

These longitudinal inserts P10 are arranged between two longitudinal grooves, in this case substantially in the centre of the longitudinal rib P21, so that the first side wall P11 of the insert and said second side wall P12 of the insert are joined together with the compound M2 forming the tread.

Composite molding element PC2 shown in fig. 4 differs from composite molding element PC1 in that insert P10 is disposed at the edge of longitudinal rib P21 at the boundary between longitudinal rib P21 and longitudinal tread groove P20.

Only the first side wall P11 or the second side wall P12 of the insert is then brought into engagement with compound M2.

It can be seen that the bottom of the tread groove P20 of the composite profiled element PC2 can be formed here by the first compound M1 of the bottom layer P14.

It goes without saying that the distinctive features of the two composite profiled elements PC1 and PC2 can be combined together to form a composite profiled element that comprises both an insert provided in the central portion of the rib and an insert provided at the edge of the rib, each of these inserts being made of the same first compound M1 as the bottom layer P14.

The extrusion head according to the invention has been developed so that composite profiled elements of the type shown in fig. 3 and 4 can be produced. However, as will be seen subsequently, it allows for a variety of alternative forms of insert to be manufactured.

Fig. 5 and 6 show the extrusion head 2 according to the first embodiment of the present invention, viewed from the side of the lower wall 20.

Upstream (in the sense of the longitudinal direction DL) of the first forming blade 32, called "upstream forming blade 32", an upstream extruder (not shown) in which the first compound M1 is processed leads via an upstream extrusion duct 31 to the lower wall 20.

The transverse profile of the upstream forming blade 32 is designed to shape the first forming element P1 intended to form the bottom layer P14, the upstream forming blade 32 defining with the radially outer wall 11 of the roll 10 a gap known as "upstream gap". The profiled element P1 is preferably of the type shown in fig. 3 and preferably extends continuously in the transverse direction DT.

Downstream of the upstream forming blade 32 and upstream of a second forming blade 42, called "downstream forming blade 42", a downstream extruder 40 (not shown) in which the compound M2 is processed opens into the inner wall 20 via a downstream extrusion duct 41.

Thus, immediately downstream of the upstream forming blade 32 and, suitably, upstream of the downstream forming blade 42, the flow of compound M2 conveyed from the downstream extrusion duct 41 comes into contact, as soon as it leaves the downstream extrusion duct 41, with the radially outer portion of the first forming element P1 forming the bottom layer P14, in this case more specifically the flow of compound M2 comes into contact with the radially outer surface of said bottom layer P14. The convergence of these two flows is likely to be a source of turbulence liable to alter the profile of the first forming element P1 (in particular the bottom layer P14), which is why it is necessary to adjust the transverse profile of the upstream forming blade 32 accordingly.

The gap between the downstream forming blade 42 and the radially outer surface 11 of the roll 10 is used to determine the transverse profile of the second forming element P2 and to perfectly join the forming elements P1 and P2 to obtain the composite forming elements PC, PC 1.

From upstream to downstream, there is thus again indeed:

an upstream extrusion unit 3 comprising an upstream extrusion duct 31 disposed at the outlet of the upstream extruder 30 and open to the lower wall 20, to be able to convey a flow of the first rubber compound M1,

an upstream forming blade 32, arranged in a transverse direction downstream of the upstream extrusion duct 31, to determine a first transverse profile of a first forming element P1 formed by the flow of said first rubber compound M1,

a downstream extrusion unit 4 comprising, downstream of the upstream forming blade 32, a downstream extrusion duct 41 arranged at the outlet of the downstream extruder 40 and open to the lower wall 20, to enable the delivery and combination in a flow convergence zone of the flow of the second rubber compound M2, and of the flow of the second compound with the flow of the first rubber compound M1, and

downstream forming blades 42, arranged in the transverse direction downstream of the downstream extrusion duct 41 and the flow convergence zone, to determine the transverse profile of the composite forming element PC formed by the first rubber compound M1 and the second rubber compound M2.

Furthermore, in order to prevent the flow of the second compound M2 from deforming one or more inserts P10 in the flow meeting area, the extrusion head 2 is advantageously provided with at least one channel 5, preferably with several channels 5, preferably with as many channels 5 as there are actual inserts P10, and as will be described in detail below, said channels 5 will form flow-dividing ducts which (each duct) catch some of the first compound M1 intended to form said insert P10 and convey this portion of the first compound M1, while remaining at least temporarily spaced from the second compound M2 over a portion of the longitudinal path between the upstream forming blade 32 and the downstream forming blade 42, to allow this portion of the first compound M1 (which is intended to form the insert P10) to bypass the meeting area without coming into contact with the second compound M2, but at the same time still maintaining continuity in material with the bottom layer P14 and allowing this portion of first compound M1 to come into contact with the second compound M2 only subsequently in the downstream gap, which is located outside the meeting region, sufficiently downstream of it.

To this end, the extrusion head 2 preferably comprises at least one channel 5 formed by

walls

53, 54, 55, said

walls

53, 54, 55 extending in the longitudinal direction DL between the upstream forming blade 32 and the downstream forming blade 42 from an upstream end 51 of the channel 5, upstream of the meeting region where the flow of the first rubber compound M1 and the flow of the second rubber compound M2 are joined, up to a downstream end 52 of said channel 5, downstream of said flow meeting region and upstream of the downstream forming blade 42.

Said

walls

53, 54, 55 of the channel together form a concave surface open towards the inside of the extrusion chamber and are arranged in such a way that:

on the one hand, a portion of the flow of the first rubber compound M1 (which portion is intended to form the insert P10 in the composite profiled element PC) can enter the channel 5 and advance longitudinally along said channel 5 without coming into contact with the second rubber compound M2, but at the same time maintaining continuity in the material with the bottom layer P14 of the first profiled element P1, said bottom layer P14 being to be shaped in the upstream gap defined by the upstream profiled blade 32,

on the other hand, the bonding of the one or more side walls P11, P12 of the insert P10 with the second rubber compound M2 occurs (only) subsequently in the downstream gap defined by the downstream forming blade 42.

Advantageously, therefore, the invention makes it possible to produce successively a first confluence (first confluence of flows) between the first compound M1 and the second compound M2, where the second compound M2 is in contact for the first time with the first compound M1, more particularly with the bottom layer P14 forming the first portion of the first forming element P1, and a second different confluence (second confluence of flows); said second confluence is shifted downstream with respect to the first confluence, in which the same second compound M2 is in contact (for a second time) with the second element of the same first forming element P1, in this case with the insert P10 concerned, said insert P10 not being exposed before the second confluence, since they are protected by their respective channels 5, which channels 5 separate them from said second compound M2.

Preferably, the

walls

53, 54, 55 of the channel 5 may extend from the upstream gap up to the downstream gap, covering substantially the entire distance separating the upstream forming blade 32 from the downstream forming blade 42 in the longitudinal direction. This would then provide the most permanent and therefore the most effective protection of feasibility for the insert P10 with respect to the second compound M2.

Preferably, as shown in fig. 5, 6, 7 and 8, or in fig. 16 and 17, the extrusion head 2 comprises at least one channel 5 extending in the longitudinal direction DL, the upstream end 51 of said channel 5 being arranged in the continuation of the discharge opening 320 formed in the upstream forming blade 32, and the downstream end 52 thereof opening into the gap defined by the downstream forming blade 42 and the radially outer surface 11 of the roll 10, just upstream of the downstream forming blade 42.

The channel 5 may take the form of a tube, preferably having a substantially triangular or trapezoidal cross-section, comprising a first side wall 53 supported by a first partition 530, a second side wall 54 supported by a second partition 540, and a wall 55 forming the bottom of the channel.

The

walls

53, 54 and 55 together form a continuous concave surface open radially towards the inside, the concavity of which faces the radially outer wall 11 of the roller 10.

The

walls

53, 54 and 55 of the channel 5 form a duct which opens at its two ends, upstream end 51 and downstream end 52, in the form of a gutter or inverted hull.

At the upstream end 51 of the channel 5, a spacer 530 is preferably attached to the downstream side 321 of the upstream profiled blade 32, and the radially lower edge of the spacer 530 is flush with the profile of the upstream profiled blade 32. The upstream profiled blade 32 therefore has, at this upstream end 51 of the channel 5, a transverse profile in the form of a discharge opening 320, the downstream portion of which is arranged in continuity with the wall 55 forming the bottom of the channel to promote the flow of the compound M1 in the channel 5.

At the downstream end 52 of the channel 5, the channel 5 opens directly into the gap formed by the downstream forming blade 42 and the radially outer wall 11 of the roll 10. The channel 5 shown in fig. 5 and 6 and, where appropriate, in fig. 16 and 17 is constructed in such a way that the wall 55 forming the bottom of the channel 5 is arranged radially at the same height position as the radial position here at the downstream forming blade 42. Conversely, at this downstream end 52, the

spacers

530 and 540, which support the

side walls

53 and 54 in the channel 5, extend radially towards the inside at a lower radial position than the position of the downstream forming blade 42.

However, if it is not necessary for the insert P10 to be present on the surface of the tread, it is entirely possible to arrange the wall 55 forming the bottom of the channel 5 at a lower radial position than the radial position of the downstream forming blade 42, at the downstream end 52 of the channel 5.

Thus, while maintaining continuity in the material with the compound M1 forming the bottom layer P14, the portion of compound M1 entering the channel 5 flows directly from the upstream end 51 to the downstream end 52, without coming into contact with the second compound M2, so that the pressure variations observed at the junction of the flow of compound M2 with the flow of compound M1 do not cause any damage to the profile of the compound M1 given to the channel 5 already entered and intended to form the insert P10.

The shaping of the insert P10 takes place during the whole advancement of the compound M1 along the channel 5 and corresponds to the profile of the insert P10 of the composite profiled element PC according to the profile of the radial plane passing through the downstream end of the channel 5. Thus, the bonding of the side walls P11 and P12 of the insert with the compound M2 forming the tread takes place directly in the downstream gap defined by the downstream forming blade 42 and the radially outer wall 11 of the roller, and the profile of the insert is not modified.

The manner in which the pressure in the channel 5 varies can be controlled by adjusting the angle formed by the

side walls

53 and 54 with respect to the longitudinal direction DL. These two walls converge towards each other in the direction from upstream towards downstream, for example at an angle of about 5 ° to the longitudinal direction, so that the cross section of the channel in a radial plane or in a plane perpendicular to the longitudinal direction decreases continuously in the direction from the upstream end 51 towards the downstream end 52 of the channel, and so that said cross section is minimal at the downstream end 52.

In the case shown in fig. 5 and 6, the cross-section of the channel at the downstream end 52 has a substantially triangular shape corresponding to the preferred embodiment of the insert. However, the shape of the cross section is not limited and may be arbitrarily changed.

According to this first embodiment of the invention, the channel 5 shown in fig. 5 and 6 occurs between two projections 420 of the downstream forming blade 42. The protrusions 420 are intended to form the tread grooves P20 of the composite molding element shown in fig. 3. This arrangement means that the insert P10 is disposed substantially centrally of the longitudinal rib P21.

Fig. 7 and 8 show a second embodiment of the invention which makes it possible to produce a composite profiled element of the type shown in fig. 4 and in which it is desired to arrange inserts P10 at the boundary between the longitudinal rib P21 and the tread groove P20.

The forming head then comprises at least one separating element 6 between the upstream and downstream forming blades 42, said separating element 6 being arranged in the longitudinal continuation of the projection 420 of the downstream forming blade 42 and extending from the upstream forming blade 32 up to the downstream forming blade 42. The dividing element 6 divides the second extrusion conduit 41 into subducts 410.

The side walls of one or more channels 5 then coincide with the

side walls

63, 64 of the separating element 6 and the walls forming the channels 5 as described above for the first embodiment of the invention apply mutatis mutandis with respect to the layout of the first forming blade 32 and the second forming blade 42, respectively.

At the protrusion 420 of the downstream forming blade 42, a radially inner wall 421 of the protrusion is provided at the same radial position as the radially inner wall 65 of the partition member 6. This wall 65 extends downstream of said projection 420 and it occupies the same radial position as the wall of the upstream forming blade 32 at the position where it meets the upstream forming blade 32.

This means that the various forms of the embodiments of the invention can be combined in various ways without thereby departing from the spirit of the invention.

Likewise, a machine for co-extruding profiled elements consisting of an assembly of profiled elements formed with different rubber compounds, comprising a cylindrical roller and an extrusion head according to the invention, can be considered to fall within the scope of protection of the present application.

To reproduce the composite profiled element PC1 as shown in fig. 3, the second compound M2 was combined with each of the side walls P11 and P12 of at least one insert P10.

Also, in order to reproduce the composite profiled element PC2 as shown in fig. 4, the second compound M2 was combined with only one side wall P11 or P12 of at least one insert.

In order to achieve a better shaping of the insert, the walls are arranged in such a way that the cross section formed by said walls of the insert and the base P13 on a radial plane passing through the axis 12 decreases between the outlet of the first gap and the inlet of the second gap.

In order to obtain a triangular shaped insert P10, the

walls

53, 54, 55 are arranged in such a way that, at the entrance of the downstream gap, the cross section formed by said walls of the insert and the base P13 on a plane perpendicular to the longitudinal direction is triangular in shape.

Likewise, the

walls

53, 54, 55 of the channel 5 are arranged in such a way that the cross section formed by said walls of the insert P10 and the base P13, on a plane perpendicular to the longitudinal direction, decreases between the outlet of the upstream gap and the inlet of the downstream gap.

The forming wall may be fixed.

Alternatively, the lower wall of the extrusion head may have a concave shape with a cylindrical profile extending in a transversal direction with a given axis, the circumferential direction of said cylindrical profile coinciding with the longitudinal direction DL defining the advancement direction of the profiled element through the machine. The profiled wall may then be formed by a cylindrical roller 10, said cylindrical roller 10 being rotatable about an axis 12 coinciding with the axis of the lower wall 20, and the radially outer wall 11 thereof forming said profiled wall.

It can be seen here that the first profiled element P1 has no discontinuity in the transverse direction DT.

Furthermore, it is preferred that the total width of the first profiled element P1, more particularly of the bottom layer P14 thereof formed as a single piece (in said transverse direction DT) accounts for more than half, more preferably at least 70%, of the total width of the composite profiled elements PC, PC1, PC2 obtained at the outlet of the downstream gap.

The underlayer P14, formed of a material harder than the material forming the second profiled element P2 and therefore the tread (i.e. the second compound M2), in this case the first compound M1, actually needs to occupy a width sufficient to effectively contribute to the proper mechanical integrity of the tyre, together with the underlying reinforcing plies forming an object resembling a composite beam in the radial thickness of the tyre.

Furthermore, as mentioned above, the insert P10 is formed using the first material M1 and is continuous in material with the rest of the profiled element P1, more specifically with the bottom layer formed as a single piece over the width mentioned above.

Whatever the rest of its embodiment, the composite profiled elements PC, PC1, PC2 according to the invention can advantageously be used to cap the crown of a green tyre with the aim of forming the tread of the tyre after shaping and vulcanisation.

Another aspect of the present invention, that is, the use of the

discharge ports

71, 72 to produce edge rubber in the tread groove P20, will now be described. This aspect of the invention can effectively and advantageously complement the creation and arrangement of the insert P10 as obtained using the channel 5 described hereinbefore.

This aspect of the invention will be described in more detail with reference to fig. 9 to 17, but is not to be construed as limiting the invention in any way.

Of course, for convenience of description, certain elements that are the same as or similar to elements already described in the foregoing will be assigned the same reference numerals and furthermore do not necessarily have to be the subject of further detailed description.

Fig. 10 shows a third alternative form of a third composite profiled element PC3 according to an embodiment, the third composite profiled element PC3 comprising a first profiled element P1 and a second profiled element P2; the first forming element P1 is made of a first compound M1 intended to form a bottom layer; said second forming element P2 is made of a second compound M2, intended to form a tread. The profile of the tread comprises longitudinal grooves P20 interposed between longitudinal ribs P21.

This third composite profiled element PC3 also includes at least one edge rubber P3, said edge rubber P3 including an edge rubber P31 disposed in the bottom of the tread groove and associated with at least one side edge rubber P30 covering the side walls of the tread groove.

The edge rubber P3 was formed from the third compound M3.

The third compound M3 may be of the same kind as compound M1, or preferably of a different kind.

Where appropriate, the third compound M3 may be of the same kind as the second compound M2.

The fourth composite profiled element PC4 shown in fig. 11 comprises a longitudinal insert P10 made of compound M1, said longitudinal insert P10 having an overall shape of a triangle and extending in the radial direction DR from an imaginary base P13 located on the radially outer surface of the bottom layer P1 up to the radially outer surface of the second profiled element P2. These longitudinal inserts P10 are disposed along the edge of the longitudinal rib P21 at the boundary between the longitudinal rib P21 and the longitudinal tread groove P20, so that the side wall P11 or P12 of the insert forms the edge of the tread groove. The triangular shape of the insert P10 is non-limiting and, as will be seen later, it is entirely possible to produce inserts of different shapes, provided that the base of the insert is in material continuity with the radially outer surface of the second forming element forming the bottom layer.

It can be seen that only the wall of the insert P10 opposite the wall forming the edge of the tread groove is then bonded to the second compound M2.

The edge rubber P3 is intended to cover the sidewalls of the insert P10 and the bottom of the tread groove with the third compound M3.

This third compound M3 will be able to be formed from a different kind of composition from the one forming the compound M1 or M2, or here preferably it may also be formed from the same kind of composition as the compound M2.

It is self-evident that the different features of these two composite molding elements PC3 and PC4 can be combined to form a composite molding element comprising an edge rubber covering the walls of the tread groove adjacent to the insert and the walls of the tread groove free of the insert.

An alternative form of extrusion head 2 corresponding to that of figures 12 to 17 has been developed so that composite profiled elements PC3, PC4 of the type shown in figures 10 and 11 can be produced.

As before, the extrusion head 2 comprises an upstream extruder 30 (visible in fig. 9) in which the compound M1 is processed, said upstream extruder 30 being conveyed towards the lower wall 20 via an upstream extrusion duct 31 arranged upstream (in the sense of the longitudinal direction DL) of the upstream forming blade 32.

The transverse profile of the upstream forming blade 32 is designed to shape the first forming element P1 intended to form the bottom layer P14, the upstream forming blade 32 forming a gap with the radially outer wall 11 of the roll 10. The first forming element P1 may be of the type shown in fig. 3 and extend continuously in the transverse direction DT.

Downstream of the upstream forming blade 32 and upstream of the downstream forming blade 42, the downstream extruder 40 (visible in fig. 9) in which the compound M2 is processed leads via a downstream extrusion duct 41 to the lower wall 20.

Thus, immediately downstream of the upstream forming blade 32 and, suitably, upstream of the downstream forming blade 42, the flow of compound M2 conveyed from the downstream extrusion duct 41 comes into contact with the radially outer part of the first forming element P1 forming the bottom layer as soon as it leaves the downstream extrusion duct 41. The convergence of these two flows is likely to be a source of turbulence that tends to alter the profile of the bottom layer, which is why it is necessary to adjust the transverse profile of the upstream forming blade 32 accordingly.

As previously described, the downstream gap defined between the downstream forming blade 42 and the radially outer surface 11 of the roll 10 serves to determine the transverse profile of the composite forming element PC formed by the assembly of rubbers M1 and M2 and to perfectly join the forming elements P1 and P2.

As in the first and second alternative forms of embodiment described above with reference to fig. 5 to 8, the downstream forming blade 42 preferably comprises at least one protuberance 420 intended to form a longitudinal tread groove P20.

However, unlike these previous alternatives, in addition to the downstream extruder 40, the downstream extrusion unit 4 is also associated with a secondary extruder 70 visible in fig. 9, said secondary extruder 70 supplying the third compound M3.

The auxiliary extruder 70 is connected via an internal conduit passing through the extrusion head 2 up to an extrusion conduit 71, said extrusion conduit 71 leading to the upstream portion of the projection 420 of the downstream forming blade 42. The auxiliary extrusion duct 71 is formed by two side walls 720 substantially parallel to the side walls 422 of the downstream portion of the projections and an upstream wall 73 perpendicular to the longitudinal direction. These walls are carried by side spacers 721 and upstream spacers 731.

The cross section of the auxiliary extrusion duct 71 in a radial plane of the section perpendicular to the longitudinal direction DL defines an imaginary surface in which the entire cross section of the downstream portion in which the protrusion 420 can be incorporated on the same plane. It should be noted that the downstream edge 723 of the side barrier 721 and the upstream surface (not visible) of the boss 420 are completely coincident with this cross-sectional plane.

At least one of the sidewalls 720 is spaced from the sidewall 422 of the downstream portion of the protrusion 420 by a distancedTo define a side discharge opening 72 of width d between the two walls, the compound M3 from the auxiliary extruder 70 is extruded through the side discharge opening 72 to form a side edge rubber P30.

The radially lower edge 722 of the sidewall 720 and the radially lower edge 732 of the upstream wall 730 are included in a plane substantially perpendicular to the radial direction DR. The plane is spaced from the radially inner wall 421 of the protrusion 420 by a distancee. Moreover, the opening in said radial section plane between the radially lower wall 421 and the radially lower edges of the

walls

720 and 730 defines a height ofeVia the lower discharge port 73, the compound from the auxiliary extruder 70 is extruded to form an edge rubber at the bottom of the tread groove P31.

The side discharge port 72 and the lower discharge port 73 communicate with each other to ensure continuity in material between the side edge rubber P30 and the groove bottom edge rubber P31.

Likewise, the radially lower spaces of the

discharge openings

72, 73 preferably remain open and face the flow of material from upstream and into the gap defined by the downstream forming blade 42 and the radially outer surface 11 of the roll 10.

Distance between two adjacent platesdAndethe values of (a) define the thicknesses of the side edge rubber P30 and the lower edge rubber P31, respectively. Typically, these values are about one milliMeter and preferably below this value.

The preferred flow direction of material M3 exiting extrusion conduit 71 is indicated by the heavy arrows.

The choice between one or both side openings depends on the configuration of the composite profiled element PC, PC3, PC4 desired to be produced, in particular whether it is desired to cover only one or both sides of the tread groove with edge rubber P3 (see fig. 10 or fig. 11). Thus, fig. 14 shows an auxiliary extrusion duct 71 comprising two side openings 72; while figure 15 shows an auxiliary extrusion duct 71 comprising only one side opening 72.

Extruding the edge rubber P3 in the downstream forming blade just upstream of the protuberance 420 makes it possible to avoid the profile of this rubber being disrupted by the flow-through effect of the flow of compound M1 and of compound M2 entering the downstream gap defined by this downstream forming blade 42. Since the auxiliary extrusion conduit is located a few millimetres away from the outlet of the composite profiled element, the pressure in the material is close to zero and the rubber movement which tends to change the edge rubber profile is negligible.

The fourth embodiment of the invention is particularly suitable for producing a composite profiled element PC4 of a fourth type corresponding to the type shown in fig. 11, which corresponds to an insert P10 provided at the boundary of one or both side edges of the tread groove P20.

An extrusion head 2 according to this embodiment of the invention is shown in fig. 16 and 17. It differs from the extrusion head for producing the third composite profiled element PC3 described above in that it comprises at least one separating element 6, said separating element 6 being arranged in the longitudinal continuation of the projection 420 of the downstream forming blade 42. The separating element 6 extends from the upstream profiling blade 32 up to the downstream profiling blade 42 and divides the downstream extrusion duct 41 into subducts 410.

At the downstream forming blade 42, the side wall 63 of the partition element 6 is arranged in continuation of the side partition 721 of the auxiliary extrusion duct 71, and the radially inner wall 64 of the partition element 6 is arranged radially at substantially the same height as the radially lower edge 732 of a partition 731, said partition 731 supporting the upstream wall 730 of the outlet of the auxiliary extrusion duct 71. The upstream spacer 731 supporting said upstream wall 730 may thus advantageously coincide with the downstream end of the partition element 6.

At the location where it meets the upstream forming blade 32, the radially inner wall 64 of the separating element is arranged radially at the same level as the wall of the upstream forming blade 32.

Preferably, the extrusion head 2 further comprises at least one channel 5, said channel 5 extending in the longitudinal direction from the upstream forming blade 32 up to the downstream forming blade 42.

Such a channel 5 preferably has the characteristics already described with reference to fig. 1 to 8, for the same purpose of protecting the insert P10 from the second compound M2.

Such a channel 5 preferably takes the form here of a duct having a substantially triangular or trapezoidal cross section, said duct comprising: sidewalls 53 supported by spacers 530; the other side wall, which is arranged facing the preceding side wall, is formed by the side wall 63 of the separating element 6; and a wall 54 forming the bottom of the channel. The

walls

53, 63 and 54 together form a continuous concave surface open radially towards the inside, the concavity of which faces the radially outer wall 11 of the roller 10. These walls define a conduit that opens at its two ends, upstream end 51 and downstream end 52, in the form of a gutter or inverted hull.

At the upstream end 51 of the channel 5, a spacer 530 is attached to the downstream side 321 of the downstream profiled blade 32, and the radially lower edge of the spacer 530 is flush with the profile of the upstream extrusion blade 32. The upstream profiled blade 32 therefore has, at this upstream end 51 of the channel 5, a transverse profile in the form of a discharge opening 320, the downstream portion of which is arranged in continuity with the wall 55 forming the bottom of the channel to promote the flow of the compound M1 in the channel 5.

At the downstream end 52 of the channel 5, the channel 5 opens directly into the gap formed by the downstream forming blade 42 and the radially outer wall 11 of the roll 10. The channel 5 shown in fig. 16 and 17 is constructed in such a way that the wall 55 forming the bottom of the channel 5 is arranged radially at the same height position as the radial position here at the downstream forming blade 42. Conversely, at this downstream end 52, the spacers 530 supporting the side walls 53 in the channel extend radially towards the inside at a radial position lower than that of the downstream forming blade 42.

If it is not necessary for the insert to be present on the surface of the tread, it is entirely possible to arrange the wall 55 forming the bottom of the channel 5 at a radial position lower than that of the downstream forming blade 42, at the downstream end 52 of the channel 5.

Thus, while maintaining continuity in the material with the compound M1 forming the bottom layer, the portion of compound M1 entering the channel 5 flows directly from the upstream end 51 to the downstream end 52, without coming into contact with the compound M2, so that the pressure variations observed at the junction of the flow of compound M2 with the flow of compound M1 do not cause any damage to the profile of the compound M1 imparted to the channel 5 already entered and intended to form the insert P10.

The shaping of the insert P10 takes place during the whole advancement of the first compound M1 along the channel 5 and corresponds to the profile of the insert P10 of the composite profiled element PC according to the profile of a radial plane passing through the downstream end of the channel 5. Thus, the bonding of the wall of the insert opposite to the wall of the insert forming the tread groove wall (P11 or P12) to the compound M2 forming the tread takes place directly in the gap formed by the downstream forming blade 42 and the radially outer wall 11 of the roller, and the profile of the insert is not modified.

side walls

53 and 63 with respect to the longitudinal direction DL. These two walls converge towards each other in the direction from upstream towards downstream, making an angle of, for example, about 5 ° with the longitudinal direction, so that the cross section of the channel, in a radial plane or in a plane perpendicular to the longitudinal direction, decreases continuously in the direction from the upstream end 51 towards the downstream end 52 of the channel, and so that said cross section is minimal at the downstream end 52.

The thickness of the spacers 530 supporting the side walls 53 in the channel is small so as not to disrupt the material flow flowing on both faces thereof. A thickness of less than 2mm, preferably less than 1mm, appears suitable.

In the case shown in fig. 16 and 17, the cross-section of the channel at the downstream end 52 has a substantially triangular shape corresponding to the preferred embodiment of the insert. However, the shape of the cross section is not limited and may be arbitrarily changed.

Extrusion of compound M3 via

discharge ports

72 and 73 allowed edge rubber P3 to be applied to the sides of the insert and the bottom of the tread groove.

Here it can be seen that the downstream end 52 of the channel 5 is provided slightly upstream of the side opening 72, so that the side edge P11 of the insert P10 is formed before it receives the edge rubber P3.

Thus, more generally, an extrusion head 2 according to the invention comprising one or more of the above-mentioned channels 5 may be preferably characterized in that: downstream forming blade 42 includes at least one protuberance 420 to form longitudinal tread groove P20 in composite forming element PC; the channel 5 is arranged in such a way as to provide an insert P10 at the border of the side edges of the tread groove P20, so that the side walls P11, P12 of the insert P10 form the edges of the tread groove; the auxiliary extrusion duct 71 comprises

discharge ports

72, 73 arranged at the edge of said protrusion 420 upstream of said protrusion 420, forming one or more side discharge ports 72, and a lower discharge port 73, enabling the application of an edge rubber P3 to the tread groove P20 of the composite profiled element PC1, PC2, said edge rubber P3 comprising a groove bottom edge rubber P31 applied on the bottom of the tread groove through the lower discharge port 73, and at least one side edge rubber P30 applied on the side walls P11, P12 of the insert P10 through the side discharge port 72.

Advantageously, the combined use of the

discharge openings

72, 73 and of one or more channels 5 allows to precisely cover the side walls of the insert P10, more generally the walls of the tread groove P20, with a thin flat edge layer having a suitably controlled additional thickness and which may preferably have the same composition as the second compound M2.

Of course, the invention relates to a corresponding method and alternatives thereof.

The invention therefore relates to a method for co-extruding composite profiled elements PC, PC1, PC2, PC4, consisting of an assembly of profiled elements P1, P2 formed with different rubber compounds M1, M2, wherein the following steps are carried out by using a co-extrusion machine 1, said co-extrusion machine 1 comprising an upstream extruder 30 and a downstream extruder 40 conveying to an extrusion cavity formed by a space between a lower wall 20 of an extrusion head 2 and a profiled wall 11 arranged opposite to the lower wall 20, wherein:

conveying upstream of the first forming blade 32, called "upstream forming blade" 32, by using the upstream extruder 30, the first rubber compound M1 coming out of the upstream extrusion duct 31 in the lower wall 20 of the extrusion head 2,

-producing a first forming element P1 formed by a first rubber compound M1 in an upstream gap defined by an upstream forming blade 32 and a forming wall 11, said first forming element P1 comprising at least a first forming element portion intended to form a bottom layer P14 and at least a second forming element portion intended to form a longitudinal insert P10, the base portion P13 of said longitudinal insert P10 being in material continuity with said bottom layer P14, and said longitudinal insert P10 forming a bulge on said bottom layer P14, the side walls P11, P12 of said bulge extending outwards with respect to the outer surface of said first forming element P1,

conveying the second rubber compound M2 downstream of the upstream shaping blade 32 via a downstream extrusion duct 41 opening into the lower wall 20 of the extrusion head 2, and joining the second rubber compound M2 with the radially outer surface of the first shaping element P1 at a region where the flow of the second rubber compound M2 meets the flow of the first rubber compound M1, by using a downstream extruder 40,

passing the first forming element P1 and the second rubber compound M2 through a downstream gap, provided downstream of the downstream extrusion duct 40 and defined by the second forming blade 42 and the forming wall 11, called "downstream forming blade" 42, to produce a composite forming element PC formed by the first rubber compound M1 and the second rubber compound M2.

In this method, according to the invention, the portion of the first rubber compound M1 intended to form the insert P10 circulates between the

walls

53, 54, 55 of the channel 5, said

walls

53, 54, 55 extending in the longitudinal direction DL between the upstream forming blade 32 and the downstream forming blade 42 from the upstream end 51 of said channel 5 up to the downstream end 52 of said channel 5, said upstream end 51 being upstream of the flow of the first and second rubber compounds M1 and M2 meeting, said downstream end 52 being downstream of said meeting flow and upstream of the downstream forming blade 42, said

walls

53, 54, 55 of the channels jointly forming a concave surface open towards the inside of the extrusion cavity and being arranged in such a way that the portion of the first rubber compound M1 entering the channel 5 and intended to form the insert P10, when proceeding longitudinally along the channel 5, maintains continuity in material with the underlayer P14 and does not come into contact with the second rubber compound M2, so that the bonding of one or more side walls P11, P12 of said insert P10 with the second rubber compound M2 then takes place in the downstream gap defined by the downstream forming blade 42 and the forming wall 11.

Furthermore, the downstream forming blade 42 preferably comprises at least one protuberance 420 to form a longitudinal tread groove P20 in the composite forming element PC, and an insert P10 is placed at the border of the side edges of said tread groove P20, so that the side walls P11, P12 of said insert P10 form the edges of said tread groove, wherein the third rubber compound M3 is conveyed by using a secondary extruder 70 via a secondary extrusion duct 71 opening into the upstream portion of the protuberance 420, said secondary extrusion duct 71 comprising

discharge openings

72, 73 arranged at the edges of said protuberance 420, said

discharge openings

72, 73 forming one or more side discharge openings 72, and a lower discharge opening 73, so that it is possible to apply an edge rubber P3 in the tread groove P20 of the composite forming element PC, PC1, PC2, PC4, said edge rubber P3 comprising a groove bottom edge rubber P31, P31 applied to the bottom of the tread groove through the lower discharge opening 73, And at least one side edge rubber P30 applied to the side walls P11, P12 of the insert P10 through the side discharge opening 72.

Preferably, the downstream end 52 of the channel 5 is disposed upstream of the side discharge port 73 so that the side walls P11, P12 of the insert P10 are formed before it receives the edge rubber P3.

Preferably, as shown in fig. 11, the edge rubber P3 is formed using a third rubber compound M3 having the same composition as the second rubber compound M2.

Advantageously, it is thus possible to obtain a composite profiled element PC, PC4 in which the insert P10 is slightly "offset" laterally (in the transverse direction DT) within the second rubber compound M2 making the respective block of the tread (that is to say, exactly within the block of the tread), while at the same time a thin thickness of the side edge rubber P30 is made possible thanks to the side discharge openings 72, so that said insert P10 close to the tread groove P20 remains in a position in which said insert P10 does effectively reinforce the block made of the second compound.

As an illustration, the thickness of the side edge rubber P30 covering the side walls P11, P12 in the insert P10 may be about 2 mm.

Specifically, depending on whether it is chosen to cover the side walls P11, P12 of the insert P10 with a thin layer of edge rubber P31 made of the second compound M2 conveyed by the auxiliary extruder 70 and the outlet 72, or with a thick layer (in terms of transverse direction) of the second compound M2 conveyed by the downstream extruder 40, the insert P10 can be disposed laterally as required in the blocks of the tread, into which the depth (in terms of transverse direction DT) of the insert P10 will be freely defined by the dimensions of the opening 72 and of the downstream forming blade 42.

By way of illustration, the depth to which insert P10 is laterally disposed in a block made of second compound M2 may be between a minimum depth of 2mm (the thinner thickness that can be achieved using opening 72) and a maximum depth of 12mm (typically equivalent to half the overall lateral dimension of the tread block, typically about 25 mm).

The invention is of course not in any way restricted to the exemplary embodiments described in the foregoing, but one skilled in the art can especially separate or combine one or other of the features described above with each other, or substitute their equivalents.

Term(s) for

1 Co-extrusion machine

10 roller

11 radial outer wall of roll

12 axes of rotation of the rolls

13 discharge belt

2 extrusion head

20 lower wall

3 upstream extrusion Unit

30 upstream extruder

31 upstream extrusion pipe

32 upstream forming blade

320 discharge port

321 downstream side of upstream forming blade

4 downstream extrusion unit

40 downstream extruder

41 downstream extrusion conduit

410 sub-pipeline

42 downstream forming blade

420 bulge

421 raised radial lower wall

422 raised side wall

5 channel

Upstream end of 51 channel

52 downstream end of the channel

53 first side wall of channel

530 first spacer

54 second side wall of the channel

540 second spacer

55 form the walls of the bottom of the channel

6 separating element

63 first side wall of a separating element

64 second side wall of the partition element

65 radially inner wall of the separating element

70 auxiliary extruder

71 auxiliary extrusion pipe

72 side discharge port 1

720 auxiliary outlet duct 71 side wall

721 support the side partition of the outlet duct of the side wall 720

722 the radially lower edge of the sidewall 720

723 downstream edge of sidewall 720

73 lower discharge port

730 auxiliary outlet duct 71 upstream wall

731 upstream spacer supporting upstream wall 730

732 radially lower edge of upstream wall 730

Direction of rotation of the R roll

Transverse direction of DT

A DL longitudinal direction; direction of advance

PC, PC0, PC1, PC2, PC3 and PC4 composite molding element

P1 first Forming element (Forming bottom layer)

P10 longitudinal insert (second element constituting the first forming element P1)

First side wall of P11 insert

Second side wall of P12 insert

Base of P13 insert

Bottom layer P14 (first element constituting first forming element P1)

P2 second Forming element (Tread)

P20 longitudinal tread groove

P21 longitudinal rib

P3 edge rubbers P30 and P31

P30 side edge rubber

P31 groove bottom edge rubber

M1 first rubber Compound

M2 second rubber Compound

M3 forms a third rubber compound of the edge rubber.

Claims

1. A co-extrusion method for co-extruding a composite profiled element (PC) consisting of an assembly of profiled elements (P1, P2) formed of different rubber compounds (M1, M2), wherein the following steps are carried out by using a co-extrusion machine (1), said co-extrusion machine (1) comprising an upstream extruder (30) and a downstream extruder (40) which convey towards an extrusion cavity formed by a space between a lower wall (20) of an extrusion head (2) and a profiled wall (11) provided opposite to the lower wall (20), wherein:

-conveying a first rubber compound (M1) coming out of an upstream extrusion duct (31) in a lower wall (20) of the extrusion head (2) upstream of a first forming blade (32), called "upstream forming blade" (32), by using an upstream extruder (30),

-producing a first forming element (P1) formed by a first rubber compound (M1) in an upstream gap defined by an upstream forming blade (32) and a forming wall (11), said first forming element (P1) comprising at least a first forming element portion intended to form a bottom layer (P14) and at least a second forming element portion intended to form a longitudinal insert (P10), the base (P13) of said longitudinal insert (P10) being in material continuity with said bottom layer (P14), and said longitudinal insert (P10) forming a bulge on said bottom layer (P14), the lateral walls (P11, P12) of said bulge extending outwards with respect to the outer surface of said first forming element,

-conveying the second rubber compound (M2) downstream of the upstream forming blade (32) via a downstream extrusion duct (41) opening into the lower wall (20) of the extrusion head (2) by using a downstream extruder (40), and joining the second rubber compound (M2) with the radially outer surface of the first forming element (P1) at a region where the flow of the second rubber compound (M2) meets the flow of the first rubber compound (M1),

-passing the first forming element (P1) and the second rubber compound (M2) through a downstream gap to produce a composite forming element (PC) formed by the first and second rubber compounds (M1, M2), wherein said downstream gap is arranged downstream of the downstream extrusion duct (40) and is defined by a second forming blade (42), called "downstream forming blade" (42), and by the forming wall (11),

the method is characterized in that the portion of the first rubber compound (M1) intended to form the insert (P10) circulates between the walls (53, 54, 55) of the channel (5), said walls (53, 54, 55) extending in the longitudinal Direction (DL) between the upstream forming blade (32) and the downstream forming blade (42) from an upstream end (51) of the channel (5) upstream of the flow of the converging first and second rubber compounds (M1, M2) up to a downstream end (52) of the channel (5), said walls (53, 54, 55) of the channel jointly forming a concave surface open towards the inside of the extrusion cavity and being arranged in such a way that the portion of the first rubber compound (M1) entering the channel (5) and intended to form the insert (P10) advances in the longitudinal direction of the channel (5) upstream of the channel (5) In turn maintaining continuity in material with the bottom layer (P14) and not in contact with the second rubber compound (M2), so that the joining of one or more side walls (P11, P12) of the insert (P10) with the second rubber compound (M2) then takes place in the downstream gap defined by the downstream forming blade (42) and the forming wall (11).

2. The coextrusion process according to claim 1, wherein the walls (53, 54, 55) of the channels (5) extend from the upstream gap up to the downstream gap.

3. The co-extrusion method according to claim 1 or claim 2, wherein the downstream forming blade (42) comprises at least one protuberance (420) to form a longitudinal tread groove (P20) in a composite forming element (PC), in which method an insert (P10) is placed at the boundary of the side edges of the tread groove (P20) so that the side walls (P11, P12) of the insert (P10) form the edges of the tread groove, wherein, by using an auxiliary extruder (70), a third rubber compound (M3) is conveyed via an auxiliary extrusion duct (71) opening into the upstream portion of the protuberance (420), the auxiliary extrusion duct (71) comprising discharge openings (72, 73) provided at the edges of the protuberance (420), the discharge openings (72, 73) forming one or more lateral discharge openings (72), and a lower discharge opening (73), enabling the deposition of an edge rubber (P3) in a tread groove (P20) of a composite profiled element (PC, PC1, PC2, PC4), said edge rubber (P3) comprising a groove bottom edge rubber (P31) applied on the bottom of the tread groove through a lower discharge opening (73), and at least one side edge rubber (P30) deposited on a side wall (P11, P12) of an insert (P10) through a side discharge opening (72).

4. A method according to claim 3, wherein the downstream end (52) of the channel (5) is arranged upstream of the side discharge opening (73) so that the side walls (P11, P12) of the insert (P10) are formed before it receives the rim rubber (P3).

5. The method according to claim 3, wherein a third rubber compound (M3) having the same composition as the second rubber compound (M2) is used to form the edge rubber (P3).

6. Coextrusion process according to claim 1 or 2, wherein the cross section of the insert (P10) in a plane perpendicular to the longitudinal direction decreases between the outlet from the upstream gap and the inlet into the downstream gap, while advancing along the channel.

7. Coextrusion process according to claim 1 or 2, wherein, at the inlet into the downstream gap, the cross-section of the insert (P10) in a plane perpendicular to the longitudinal direction is triangular in shape.

8. Coextrusion process according to claim 1 or 2, wherein, at the outlet from the downstream gap, the external vertex of the insert (P10) is flush with the external surface of the composite profiled element (PC).

9. The coextrusion process according to claim 1 or 2, wherein the second compound (M2) is associated with each lateral wall (P11, P12) of at least one insert (P10).

10. The coextrusion process according to claim 1 or 2, wherein the second compound (M2) is bonded to only one of the side walls (P11, P12) of the at least one insert (P10).

11. Coextrusion process according to claim 1 or 2, wherein a first profiled element (P1) is extruded, which first profiled element (P1) has no discontinuity in a transverse Direction (DT) perpendicular to the longitudinal direction, and preferably the total width of the first profiled element (P1) in the transverse Direction (DT) amounts to more than half, more preferably at least 70%, of the total width of the composite profiled element (PC) obtained.

12. The coextrusion process according to claim 1 or 2, wherein:

the lower wall of the extrusion head has a concave shape with a cylindrical profile extending in a transversal direction with a given axis, the circumferential direction of which coincides with the longitudinal direction defining the direction of advance of the profiled element through the machine, and

-the shaped wall is formed by a cylindrical roller (10), said cylindrical roller (10) being rotatable about an axis (12) coinciding with the axis of the lower wall (20), and the radially outer wall (11) thereof forming said shaped wall.

13. A tyre formed from a composite profiled element produced by using the coextrusion process according to any one of claims 1 to 12.

14. An extrusion head (2) for extruding a composite profiled element, the composite profiled element being constituted by an assembly of profiled elements (P1, P2) formed of different rubber compounds (M1, M2), the extrusion head (2) being intended to be mounted on a co-extrusion machine (1), the profiled elements being advanced by the co-extrusion machine (1) in an extrusion cavity along an extrusion direction extending from upstream to downstream and defining a longitudinal Direction (DL), the extrusion head (2) comprising a lower wall (20) partially delimiting the extrusion cavity and comprising, from upstream to downstream of the lower wall (20) in the longitudinal Direction (DL):

-an upstream extrusion unit (3) comprising an upstream extrusion duct (31) arranged at the outlet of the upstream extruder (30) and open to the lower wall (20) to enable conveying of a flow of a first rubber compound (M1),

-an upstream forming blade (32) arranged in a transverse direction downstream of the upstream extrusion duct (31) to determine a first transverse profile of a first forming element (P1) formed by the flow of the first rubber compound (M1),

-a downstream extrusion unit (4) comprising, downstream of the upstream forming blade (32), a downstream extrusion duct (41) arranged at the outlet of the downstream extruder (40) and open to the lower wall (20) to enable the delivery of a flow of a second rubber compound (M2) and the combination thereof with a flow of a first rubber compound (M1) in a flow convergence zone,

-a downstream forming blade (42) arranged in a transverse direction downstream of the downstream extrusion duct (41) and the flow convergence zone to determine a transverse profile of the composite forming element (PC) formed by the first and second rubber compounds (M1, M2),

characterized in that said extrusion head comprises at least one channel (5) formed by walls (53, 54, 55), said walls (53, 54, 55) extending in a longitudinal Direction (DL) between an upstream forming blade (32) and a downstream forming blade (42) from an upstream end (51) of said channel (5) up to a downstream end (52) of said channel (5), said upstream end (51) being located upstream of a region where the flows of the first and second rubber compounds (M1, M2) meet, said downstream end (52) being located downstream of said region where the flows meet and upstream of the downstream forming blade (42), said walls (53, 54, 55) of the channel jointly forming a concave surface open towards the inside of the extrusion cavity and being arranged in such a way that, on the one hand, the portion of the flow of the first rubber compound (M1) intended to form the insert (P10) in the composite forming element (PC) can enter the channel (5) and be inside said channel (5) 5) But does not contact the second compound (M2), but maintains continuity in material with a bottom layer (P14) of the first forming element (P1) made of the first rubber compound (M1), said bottom layer (P14) being intended to be formed in the upstream gap defined by the upstream forming blade (32), on the other hand, the joining of one or more side walls (P11, P12) of the insert (P10) with the second rubber compound (M2) then taking place in the downstream gap defined by the downstream forming blade (42).

15. The extrusion head of claim 14, wherein: said downstream forming blade (42) comprising at least one protuberance (420) to form a longitudinal tread groove (P20) in the composite forming element (PC); the channel (5) is arranged in such a way as to provide an insert (P10) at the boundary of the side edges of the tread groove (P20), so that the side walls (P11, P12) of the insert (P10) form the edges of the tread groove; the auxiliary extrusion duct (71) comprises discharge ports (72, 73) arranged at the edges of said protrusion (420) upstream of said protrusion (420), forming one or more side discharge ports (72), and a lower discharge port (73), enabling the application of an edge rubber (P3) to the tread groove (P20) of the composite profiled element (PC1, PC2), said edge rubber (P3) comprising a groove bottom edge rubber (P31) applied on the bottom of the tread groove through the lower discharge port (73), and at least one side edge rubber (P30) applied on the side wall (P11, P12) of the insert (P10) through the side discharge port (72).